NON-ISOTHERMAL CURE KINETICS AND THERMODYNAMICS OF EPOXY FILM ADHESIVE DERIVED FROM OXAZOLIDONE MODIFIED EPOXY NOVOLAC RESIN

This work deals with the kinetic and thermodynamic evaluation of an epoxy film adhesive derived from epoxy novolac resin after incorporation of an oxazolidone ring system in the polymer backbone, using differential scanning calorimetry. The effect of polyethersulfone (PES) as the thermoplastic toughening agent, on the non-isothermal curing reaction is also studied. Non-isothermal curing reaction is captured at different heating rates viz. 3, 5, 7, and 10°C min<sup>–1</sup> and various kinetic parameters are derived from its curing behavior using the Kissinger equation. Activation energies for the systems are 139 kJ mol<sup>–1</sup> (without PES) and 142 kJ mol<sup>–1</sup> (with PES). The frequency factor and rate constant are found to be higher for the system with PES than that of the system without it. Derived kinetic parameters are used to predict the peak exothermic temperature and corresponding reaction rate, constant for different heating rates, and resulted in a very close match with the values obtained experimentally. Later, the rate constants obtained from the kinetic analysis are used to compute the thermodynamic parameters in the activated state via absolute reaction rate theory proposed by H. Eyring. Change in entropy and Gibb's free energy for the activated state complex indicates that the non-isothermal curing reaction happens in a facile manner for the system with PES than that of the system without it.